The present invention is generally directed to techniques and system for controlling propulsion, and, more particularly, to control system and method for controlling a propulsion system in a hybrid vehicle.
There are some known control strategies regarding use of electric traction in hybrid vehicles. Typically, these strategies apply to hybrids where the internal combustion engine (ICE) may not be fully capable in the sense that normal drive cycles cannot be performed with the ICE alone. One common known strategy is based on providing electrical traction assist as a boost to the ICE when required or to provide an electric start or launch, thus eliminating the need of rapidly starting the ICE to start the vehicle from a xe2x80x9cstopxe2x80x9d condition.
In some hybrid applications, the internal combustion engine may be designed to provide full driving capacity over the normal drive cycles encountered by a given vehicle. That is, the ICE is sufficiently robust to meet the driving needs of the vehicle all by itself. However, in these applications, if one adds an electric traction motor onboard the vehicle, the additional tractive effort derived from the traction motor is generally used to add more capability to the vehicle, e.g., provide a sportier vehicle from an acceleration capability point of view. Unfortunately, this type of propulsion strategy is not necessarily conducive to improving the fuel economy of the vehicle since the traction motor is not used in any systematic manner to propel the vehicle during periods of low efficiency in the ICE. As suggested above, the traction motor for such known hybrid applications is generally used during periods of high efficiency of the ICE. Therefore, although improved acceleration may be gained in such hybrid applications, fuel consumption is usually sacrificed.
An automotive ICE is typically at its lowest efficiency when torque requirements are low. Thus, to achieve greater fuel economy, it would be desirable to stop fueling the ICE when the torque requirements are low and utilize during such periods an electric machine (e.g., a traction motor) to propel the vehicle. Conversely, the ICE may be re-engaged when the torque requirements are high (and the resulting efficiency of the ICE may be relatively high) and in this case, the electric machine may be used as an alternator to charge the electric power sources onboard the hybrid vehicle.
Generally, the present invention fulfills the foregoing needs by providing in one aspect thereof a method for controlling a propulsion system in a hybrid vehicle including a traction motor and an internal combustion engine. The method allows sensing a signal indicative of vehicle torque demand. The method further allows selecting a threshold torque range indicative of conditions of relatively low vehicle torque demand. The signal indicative of vehicle torque demand is processed to determine whether the vehicle torque demand is within the threshold torque range. During conditions when the signal indicative of vehicle torque demand is within the threshold torque range, a signal is generated to activate the electric traction motor to drivingly propel the vehicle while de-engaging the internal combustion engine from propelling the vehicle. During conditions when the signal indicative of vehicle torque demand is outside the threshold torque range, a signal is generated to deactivate the electric traction motor from drivingly propelling the vehicle while re-engaging the internal combustion engine to propel the vehicle.
The present invention further fulfills the foregoing needs by providing in another aspect thereof, a control system for controlling propulsion equipment in a hybrid vehicle including a traction motor and an internal combustion engine. The control system includes a sensor coupled to sense a signal indicative of vehicle torque demand. The control system further includes memory for storing a threshold torque range indicative of conditions of relatively low vehicle torque demand. A processor is configured to process the signal indicative of vehicle torque demand to determine whether the vehicle torque demand is within the threshold torque range. During conditions when the signal indicative of vehicle torque demand is within the threshold torque range, an actuator is configured to generate a signal configured to activate the electric traction motor to drivingly propel the vehicle while de-engaging the internal combustion engine from propelling the vehicle. During conditions when the signal indicative of vehicle torque demand is outside the threshold torque range, the actuator is configured to generate a signal configured to deactivate the electric traction motor from drivingly propelling the vehicle while re-engaging the internal combustion engine to propel the vehicle.
In yet another aspect of the invention, a method is provided for controlling a propulsion system in a hybrid vehicle that includes a traction motor and a propulsion unit, such as an internal combustion engine, or a fuel cell. The method allows mapping respective regions of relatively high and low efficiency in an efficiency map for the propulsion unit. The method further allows sensing a signal indicative of said regions of relatively high and low efficiency. During conditions when the sensed signal indicates a region of low-efficiency for the propulsion unit, generating a signal configured to activate the electric traction motor to drivingly propel the vehicle while de-engaging the propulsion unit from propelling the vehicle. During conditions when the sensed signal indicates a region of high-efficiency for the propulsion unit, generating a signal configured to deactivate the electric traction motor from drivingly propelling the vehicle while re-engaging the propulsion unit to propel the vehicle.